Appropriate Technology 2
Sustainable Civilization: From the Grass Roots Up Appropriate Technology Appendix - 2 - 3 ATMOSPHERIC CONDENSER DISCUSSION At any given pressure and temperature, in a fixed volume only a limited amount of water will evaporate into vapor, the limit is referred to as the dew/saturation point. A cubic meter of normal sea level air has a mass of 1.292 kilo. A cubic meter of water vapor at sea level pressure has a mass of .804 kilo, this would occur at a temperature of 100C (212F). At 0 C (32 F), saturation point is about 1.1 gm of per cubic meter. A rule of thumb is that raising the air temperature 18°F (10°C) doubles its moisture capacity. This means that air at 86°F (30°C) can hold eight times as much water as air at 32°F. Degrees C Degrees F Gram 0 32 1.1 10 50 2.2 20 68 4.4 30 86 8.8 40 104 17.6 50 122 35.2 60 140 70.4 70 158 140.8 80 176 281.6 90 194 563.2 100 212 1126.4 Relative humidity is the percentage of water vapor present as compared to how much there could be at the present temperature. Take a typical Tucson fall day of 84 F and relative humidity of 7%. There is roughly 7% of 8.8 grams of in each cubic meter of air (.616 gram). Lower the temperature to 66 F, and relative humidity doubles to 14%. Lower the temperature to 48 F, and relative humidity again doubles, now to 28%. If we cool air without changing its moisture content, eventually we'll reach a temperature at which the air can no longer hold the moisture it contains. Then water will have to condense out of the air, forming dew or fog. The dewpoint is this critical temperature at which condensation occurs. But, water does not immediately change state as the temperature reaches the "right" point. The "Latent heat of condensation" (Lc) refers to the heat that must be removed from water vapor for it to change into a liquid. Lc=2500 Joules per gram (J/g) of water or about 600 calories per gram (cal/g) of . Specific heat is defined as the amount of heat energy required to raise 1 g of a substance by 1° Celsius. If the specific heat of air is .25 calories per gram of air per degree C change, then each degree C change in a cubic meter represents 323 calories. The specific heat of water is 1 calorie per gram per degree C. In our Tucson fall day above there was .616 grams of in a cubic meter of air. Air and water vapor together take a change of about 324 calories per degree C. We need to lower the temperature by around 40 C, or get rid of 12,960 calories of heat to reach the dew point. An additional 379 calories of heat needs to be removed to compensate for the latent heat of condensation, for a total of 13,339 calories. Assume a daily water need of 174 gallons (658.6 liters) - 658,660 grams of . In a Tucson fall day, each of us would need to "wring" all of the water out of more than a million cubic meters of air (1,069,252) - a cube 100 meters on a side. The heat to be moved is about 14 billion calories. The water portion of this number is about 450 million calories. Depending on device efficiency, SOME part of the other 1 billion calories should be able to be conserved in a heat exchanger. Increasing the pressure also changes the dew point. Double the pressure and relative humidity doubles. Assume normal atmospheric pressure of 14 PSI. Pump the fall Tucson air into a tank at 28 PSI and the relative humidity inside is now 14%. Make it 56 PSI - 28%. 102 PSI - 56%. 204 PSI - 102%, and you've got water accumulating in the bottom of the tank. A SHOCKING APPROACH If you have electricity in abundance, in 1945, South Africa's chief meteorologist, Theodore Schumann, proposed the construction of a unique cloud-condenser on top of 3,000 ft. Table Mountain on the south side of Capetown. Schumann's design comprised two large parallel fences of wire netting, one insulated and one grounded, which would be charged with a potential difference of 50-100 KV. The wire screens were to be about 150-ft. high, 9,000 ft. long, and 1 foot apart. He estimated that the electrified fence would condense as much as 30,000,000 gallons daily from "The Cloth", a perpetual cloud that crowns the peak. The fence was never built. I am unclear about the COE of per watt consumed. NASA has proposed replenishing water during a mission on Mars by using a device whith extracts water vapor from the Martian atmosphere by adsorption in a bed of type 3A zeolite molecular sieve. Using ambient winds and fan power to move atmosphere, the WAVAR adsorbs the water vapor until the zeolite 3A bed is nearly saturated and then heats the bed within a sealed chamber by microwave radiation to drive off water for collection. The water vapor flows to a condenser where it freezes and is later liquefied for use in the life support system. THERMAL STORAGE Heat energy moves by conduction (hot objects touching each other), convection (physically moving flows of heated mass, water, air, etc.), or radiation (infrared light). Water stores, conducts, and convects heat well. An advantage of water for moving heat is that although it does convect, the density difference is not so great that a low power pump cannot move "hot" water to a physically lower position. Earth tubes are an approach combining conduction and potentially convection to provide not only ventilation for a structure, but storage / moderation of heat. The "traditional" approach is a single grid of tubes, with direct exhaust from the structure. As John Hait points out in his book Passive Annual Heat Storage, use of two tubes, out the structure top, and one out the bottom, lets the structure breathe, while keeping the loss / gain of temperature due to differences between inside and outside air temperature to a minimum. Using air as the exchange medium, the tubes need to be at least 4" in diameter, and 60 feet long. Multiple tubes provide "extra" surface area to contact the earth, and exchange thermal energy. The tubes should be around 4' apart. If you could establish an insulated zone in the pipes that was "extra" cold, that area would dehumidify the air. Note, radiant heat, whether or not a human can see or sense it, travels in straight lines, and depending on the material interposed, is reflected, refracted, or absorbed. It can, for example, by using an appropriately curved reflector, be concentrated. Envision the two earth tubes passing each other, but with mirrors to concentrate radiant energy from the "hot" tube, possibly on a smaller "cold" tube, or a storage area. Black coloring "converts" light to heat of a higher temperature that would a white coloring. Nevertheless, if there is no heat exit, even a white collector will gather heat, just bouncing it around as visible light more before the frequency drops to that of heat. Although in nature, the temperature 20 feet in the earth is around the "average" of the exposed surface temperatures, this average can be adjusted. Obviously, it first requires the waterproofing and insulation of Mr. Hait's guide. Then, instead of letting the entire hot/cold timeline thru, limit the flow in your tubes to the hot/cold you want. In my situation in Arizona, I want to store "cold". Even in this climate in the summer, the nights are "cooler" than the days. I need to flow thru my soil at night to the outside, and thru my soil during the day to the home inside. While Mr. Hait and many others concentrate on air tubes, our scale experiments show that where some forced flow of temperate is desired, water filled tubes should work "better" than air filled tubes. STILLSUIT Some time ago, when I first read "Dune", I was intrigued with the "stillsuit" concept presented, and that was long before living in the desert. In the cold regions, it is accepted wisdom to dress in layers, and provide some ventilation to release body heat. But in desert climates, the typical "modern" person goes about in short sleeve clothing. Is there a better approach? The folks who make and market a cold air heat exchange mask, acknowledge they've made warm air tests, and the mask works there also to moderate temperature and humidity. (Look up turbinates and the nose of a camel for the biological inspiration.) The first daytime goal must be avoiding direct sun, and absorbing the 1 kw per hour per square yard (around 860,000 heat calories, or around 43% of the heat a human generates in an entire day). Avoiding the heat is not just a matter of avoiding direct sun, but also the heat around you. Heated ground and other objects re-radiate, and heat the ambient air. You need radiant shielding from virtually every physical object that could "illuminate" your body, and conductive / convective shielding from the heat of the air. In theory, if you avoid these radiant inputs, appropriate radiator panels could radiate heat "down" to 20 degrees below ambient temperature. Yet within your personal microenvironment, you need an air flow so that your sweat can cool your body. In theory the daily heat of a person could melt around 56 pounds of ice (7 frozen gallons - 25 liters) or cause the evaporation of just over a gallon of water (3.7 liters). Therefore if your body was in a microenvironment isolated from thermal energy exchange with the surrounding environment by a perfectly insulating suit, hourly inside your suit your would need to melt ice of just over a pint / just under a liter, or evaporate (and vent) 1/3 of a pint or about 150 ml. Add a means for one way flow of air, and thermal exchange of incoming/outgoing air, with the potential for some cooling, whether carried "ice", or electromechanical cooling, and you are creating a portable, worn environment. If you have access to cool evenings, or a home with refrigeration, "phase change" packets that melt at around 60 degrees F, vs 32 degrees for ice, are commercially available. If you need to carry along a cooling system, you probably need availability of a constant 100 watts. If you are circulating water for internal cooling, bladders at the body "hotspots" provide thermal sinks. DEFENSE TECHNOLOGY In history, the English Longbow was about 6 1/2 feet long with a draw of 160 -180 lbs., vs a modern version at 50 - 60 lbs. (My fiberglass bow is 55 lb) The range of the medieval weapon is unknown, with estimates from 180 to 249 yds. Modern versions have a useful range up to 200 yd. A 150 lb. replica longbow was able to shoot a 1.9 oz arrow 360 yd and a 3.3 oz a distance of 272 yd. Modern champion archers maintain that a hit cannot be guaranteed on an individual target at more than 80 yards with any bow. With either or both of enough arrows in the air, and a target enemy close enough together, some hit even at maximum range was almost assured. A military archer during the 14th and 15th Century was expected to shoot at least ten "aimed shots" per minute. An experienced military longbowman was expected to shoot twenty aimed shots per minute. Many war-arrows had heads that were only attached with a small blob of wax, so that if they were to be removed conventionally only the shaft would come out, leaving the head lodged in the victim which would almost certainly cause an infected wound. A weapon to be developed is a crossbow firmly mounted on a multi-axis angle adjustable frame. The bow should in theory maintain the same firing power shot after shot. If the arrows are also close in mass and aerodynamics, after just a few shots and measuring the distance travelled, a spreadsheet should be able to be worked up for any angle/distance desired. Locate side wind resistance charts and integrate and we should have arrow- artillery. The ancients had such devices, for REALLY big arrows. What they did not have was wind charts and computers. For those who fear, or plan on the loss of the knowledge and technology of higher civilization, the atlatls is another "grows on trees" weapon. It upgrades a spear from "hand to hand" status to a significant increase in thrown force and distance. While a beginner will not have much control, the world record for a throw was over 800 feet. The device is a stick about two feet long, with a handgrip at one end and a projection at the back end to fits into a cavity at the back of the spear. The spear is thrown with a sweeping arm and wrist motion. An experienced marksman could probably range out to 150 yards and be accuracte to perhaps 30 yards. For those interested and in need of a short range but larger weight launching device, there are of course catapults or trebuchet, which put trees and rocks into the arsenal. WARRANTING FURTHER INVESTIGATION Bellocq Wave Pump. This device appears to present a "new" mechanical principle, which uses pressure waves from a surface pump, rather than suction, to move water from greater depth that could be pulled by a suction pump. Reports are that the technology is very efficient in translating energy input into water flow. The inventor is Toribio Bellocq. Prior to receiving his US Patent #1,730,336 back in 1929, it is reported he had to demonstrate that the device actually worked, without any powered mechanism at the bottom of the pipe. He later improved the pump, as shown in US Patent 1,941,593 issued in 1934. The theory appears to be that the pump imparts harmonic vibrations to the water column that set up standing waves. Other discussions of standing waves include older harmonics experiments by Tesla, and more recent demonstrations of refrigeration with sound waves. In the pump, a one-way valve at the bottom admits water when the wave relieves pressure there, but prevents water from leaving at the next high pressure impact. Above sketch from the U.S. Patent Office. For so long as the present web technology remains viable, many patents can be accessed and downloaded for scientific and/or educational review at no cost. REFRIGERATION TECHNOLOGY Homemade Icyball. Ammonia evaporation / absorption refrigeration is 18th century technology. WARNING: Ammonia leaks can cause serious injury or death. There are "safer" coolants, this is presented to inspire thought as to what we should be able to do 200 or so years later. Patents on this type device date though from 1928, patent 1,740,737 and 1931, patent 1,811,523. It is basically two spheres, connected by pipe and valves. These units use liquid anhydrous ammonia as a refrigerant. The pure anhydrous ammonia is mixed with water. Heat is then applied to the ammonia solution that has been contained in a pressure vessel. The heat drives off the ammonia which then condenses in another pressure vessel. It needs to be emphasized that ammonia gas is extremely toxic and fammable. One deep breath of pure ammonia gas will KILL a human being. If you are not a mechanically inclined person who pays close attention to details, do not attempt to build one of these units. If built with quality materials and used with the proper precautions this unit can be safely operated since it is designed to contain the gas within the unit. The system which can be constructed from plans will produce 5 to 7 lb. of ice after being heated for about 90 minutes, any heat source which will result in a final generator temperature of 255 F may be used. The refrigerant solution is a mixture of distilled water and liquid anhydrous ammonia. Although anhydrous ammonia is not illegal to possess in a closed refrigeration system, it is sometimes difficult to obtain. In some states (especially in the Midwest) laws have recently been passed restricting the transfer of anhydrous ammonia due to its use in the manufacture of crystal meth. Be sure to check the situation in your state before you attempt to build one of these units! Don't scrimp on the vessels and the valves. You cannot use the brass valves available in building supply stores. Pressures of up to 250 lb. will be produced within the system. FREON CONTAINERS MUST NOT BE USED UNDER ANY CIRCUMSTANCES. ROLAMITE "Frictionless Machines from Rollers & Bands" by Harry Walton. It looks like a simple gadget made with two rollers and a steel band, but it's much more. As basic as the wheel, the lever, or the hinge, it is the only elementary machine discovered this century. As the rollers are pushed to the right, for example, they turn in opposite directions, but are always in rolling contact with the band. Nothing slides, rubs, or slips; it is always the same points that come into contact between roller and band. And a rolamite unit never needs lubrication. In tests, Rolamite devices display friction of an amazingly low order --- one to ten percent of that in the best ball and roller bearings of similar capacity. Instead of being uniform, bands can introduce more or less resistance at some point of roller travel. Holes of various shapes can be punched in them to make action easier at a predetermined point and to a precise degree. Bimetallic elements and springs, even cloth, plastic, or rubber bands can be used. Such modification can produce a snap action, sudden braking, latching, and other control functions. A sharply bent band can act as a detent. Rollers can be fitted with bulges or rubber stops for positive braking. The rollers can be of different sizes. If one is smaller, it turns faster than the other and you have a speed-changing device. Extra rollers may be added, always two at a time. Perhaps the oddest discovery is that the rollers need not be round. The different shapes of rollers give the Rolamite many additional functions. For instance, a rectangular roller can be designed to lodge against a stop in a braking mechanism. I just find this thing interesting… COOLING A variation of an evaporation / absorption cooling system uses instead of toxic chemicals under pressure, WATER in a vacuum. An air-tight water canister is placed inside the cooling container. A manually operated vacuum pump pulls a vacuum, which causes the water to boil, with an eventual temperature result of the freezing temperature of water. (In a vacuum, water boils and freezes at the same temperature.) Outside the insulated container, the system is pipe connected to a canister of the mineral zeolite. The zeolite absorbs the water vapor, up to 25% of its own weight, maintaining the vacuum, and keeping the water "boiling". Once the zeolite is saturated, the canister is replaced, and sunlight focused on the saturated zeolite can evaporate to the open air the absorbed water, making the canister available for reuse. In a different venue, a substance such as zeolite is proposed for water collection on Mars. Whether exposed to the wind, or inside a bubble with heated soil, the chemical absorbs the water vapor, which is then boiled off in a sealed container to be re-condensed for human use. SKY RADIATION COOLING Referring back to a cone for cooking, consider the same type device as a means of COOLING by radiating heat to the sky while shielding the "hot" object from incoming radiant, conductive, or convective heat around it. Potential cooling is 20 degrees F below ambient air temperature. Inside your home, near the ceiling, a sealed tank of a liquid to gas phase change material (i.e. water). The boiling temperature of water will lower as the pressure in the system is lowered. An "air space" at the top of the tank leads to coils / cooling chamber on the roof. (No liquid circulates to the roof from the ceiling tank) Shield the roof unit from direct sun, and from infrared radiation at night from surrounding objects. Water evaporated from the ceiling tank will run back, having cooled. When the roof unit is warmer than the ceiling, water will not condense, and no "reverse" heat exchange should occur. The emitter could also simply be a replacement for a skylight. Perhaps using some low power means, circulate the liquid in the ceiling tank to an under floor tank for high volume storage. Depending on local conditions, there may be a 8 μm−13 μm infrared “window” to allow radiation from bodies between 0 C and 37 C. (32-99 F), even if the ambient outside temperature is higher. A horizontal plate sees 180 degrees of sky, which probably includes neighboring trees and buildings, all of which may be radiating more than your emitter. Your emitter needs to be shaded from direct sunlight. 90 % of the sun’s radiance is at wavelengths shorter than 1.7 μm. 99 % of the sun’s radiance is at wavelengths shorter than 4 μm. 99.9 % of the sun’s radiance is at wavelengths shorter than 9 μm. 99.7 % of a 300 K blackbody’s radiance is at wavelengths longer than 4 μm. 99 % of a 300 K blackbody’s radiance is at wavelengths longer than 4.8 μm. 90 % of a 300 K blackbody’s radiance is at wavelengths longer than 7.3 μm. A cold mirror which reflected waves shorter than 4 μm and transmitted waves longer than 7 μm would allow the radiator to simply face upward through the cold mirror. The emitter must be covered with an infrared-transparent layer (i.e. polyethylene) to prevent conductive and convective transfer of ambient heat to the emitter. • The device must reject nearly all direct and indirect solar radiation falling on it. • The device must passively emit the bulk of its thermal energy as infrared radiation. • The cone of infrared emission should be centered near the zenith and not so wide that infrared radiation from hills, buildings, and vegetation is significantly absorbed by the emitter. • Its glazing must be rugged enough to be cleaned of dust, bird droppings, and debris; or the glazing must be inexpensive and replaceable. • Ultraviolet light must be prevented from degrading polyethylene glazing. A phosphor such as is used to convert blue LED radiance to white light can be used to shift the blue sky to white light. Side walls need to have right angle corner reflectors to retro-reflect exterior heat/light. Condensation - The latent heat of vaporization of water is 2.26 × 106 J/kg. A 1 m2 radiator providing 50 W/m2 of cooling can condense 1 g of in 45 s; 1 kg in 12.6 hr; or 1.9 kg per day. This amount of condensation is on a par with commercial solar stills. 10 m2 of radiators cooling 50 W/m2 in humid air could produce 19 L of water per day. People on average have a metabolic rate of 150 W. This is split between sensible heat and latent heat in the form of water vapor, the ratio depending on the ambient temperature. The load on the radiator to remove this heat requires at least 3 m2 at 50 W/m2. Net cooling in excess of this 150 W will reduce the temperature and humidity in the enclosure until it is balanced by heat leakage through the floor and walls. POWER DISCUSSION Factors: 1kw = 1.3 hp Water flow in cubic feet/second x height difference in feet divided by 8.8 = hp 1 cubic foot = 7.48 gallon Assume a two 10,000 gallon tank, one 100' higher than the other. To generate 1kw of power 1kw = 1.3hp = flow/second x 100 / 8.8 1.3 x 8.8 = flow x 100 11.44 = flow x 100 11.44 / 100 = flow .1144 cubic feet = flow .1144 cubic feet = .856 gallon/second 10,000 gallon tank / .856 = 11,682 seconds / 60 / 60 = 3.24 hours of operation for this "battery". Given the above, consider a well where the water level is more than 100 feet below the surface. A surface tank could be the size of a modest “above ground” swimming pool. A small windmill could easily during the day fill the pool, providing the evenings power for light and electronics. Moving water. Net head in feet times flow in U.S. gallons per minute = output in watts. In the family of impulse machines, the pelton is used for the lowest flows and highest heads. The cross-flow is used where flows are highest and heads are lowest. The turgo is used for intermediate conditions. Propeller (reaction) turbines can operate on as little as two feet of head. A turgo requires at least four feet and a pelton needs at least ten feet. These are only rough guidelines with overlap in applications. The cross-flow (impulse) turbine is the only machine that readily lends itself to user construction. They can be made in modular widths and variable nozzles can be used. Most developed sites now use impulse turbines. These turbines are very simple and relatively cheap. As the stream flow varies, water flow to the turbine can be easily controlled by changing nozzle sizes or by using adjustable nozzles. In contrast, most small reaction turbines cannot be adjusted to accommodate variable water flow. Those that are adjustable are very expensive because of the movable guide vanes and blades they require. If sufficient water is not available for full operation of a reaction machine, performance suffers greatly. An advantage of reaction machines is that they can use the full head available at a site. An impulse turbine must be mounted above the tailwater level and the effective head is measured down to the nozzle level. For the reaction turbine, the full available head is measured between the two water levels while the turbine can be mounted well above the level of the exiting water. This is possible because the "draft-tube" used with the machine recovers some of the pressure head after the water exits the turbine. This cone-shaped tube converts the velocity of the flowing water into pressure as it is decelerated by the draft tube’s increasing cross section. This creates suction on the underside of the runner. Centrifugal pumps are sometimes used as practical substitutes for reaction turbines with good results. They can have high efficiency and are readily available (both new and used) at prices much lower than actual reaction turbines. However, it may be difficult to select the correct pump because data on its performance as a turbine are usually not available or are not straightforward. Another type of generator used with micro hydro systems is the DC motor. Usually permanent magnet types are preferable. However, these have serious maintenance problems because the entire output passes through their carbon commutators and brushes. www.microhydropower.com As little as 100 gallons per minute (GPM) falling 10 feet through a pipe or 5 gallons per minute falling 200 feet through a pipe can supply enough power to comfortably run a small household. Turning generators with "steam" engines (water and other medium, open and closed cycle) Power can be relatively constant and regulated by using the sun to heat a storage medium, such as water in an insulated tank, which then provides power at night. In example, since closed cycle heat engines are driven by a difference in temperature, as the outdoors cools at night, and the contents of an insulated tank remain warm, the power available may actually increase. Light concentration can DRAMATICALLY increase available power. The "steam" can also be heated by growing, collecting, and burning bio fuels. Open cycle. The working fluid, which is heated to the boiling point, is channeled to expand and push a contained piston or turbine, then vented to the atmosphere. The typical working fluid is water, which may in some locations be too scarce a resource to "waste" as steam. This engine design also "wastes" the energy used to heat the water up to the steam point. Closed cycle. The working fluid, which is heated to the boiling point, is channeled to expand and push a contained piston or turbine, then routed to a condenser for cooling below the boiling point, and then pumped back into the heating chamber. In theory (Carnot) the efficiency of a heat engine is limited to nc = T1(hot gas temp) T2(cool gas temp) / T1. Historically low temperature solar engines are operated using freon or butane, with temperatures of 80 C. In a low technology situation though, it may be necessary to use only "natural" mediums. (Perhaps water in a closed system that operates partially in a vacuum, so that water boils at a lower temperature.) Food for thought. As shown by the closed cycle engine, the useable work is done by the change of state from liquid to gas, not the rise in temperature to the boiling state. Open cycle engines (think of the old steam engines) lose ALL of this initial heating energy. Closed cycle engines retain a significant portion, but must still clearly cool the medium before re-injection to the vaporization chamber. Rather than directly using steam to turn a generator, I've wondered about using steam to pressurize a tank of water (insulated from the water some way?) then using the water to spin a micro hydro system. THERMOCOUPLE Before solar cells existed, one way to make electricity was to connect a large number of thermocouples in series. This is called a thermopile. A thermocouple is made by joining two different types of wire together at the ends. If the ends are at different temperatures a current will flow through the wires. The current and voltage is very tiny, so you need to connect many hundreds or even thousands of thermocouples together to make enough electricity to light an LED (light emitting diode). Scrape about one centimetre of the ends of all of the wires until both ends are clean and shiny with no insulation or dirt. Take one wire of each metal, and twist them together at one end so that only the cleaned sections are connected. For thicker wires you will need both pairs of pliers-grab the wires together with one pair of pliers, about 12mm from the end, and twist the ends together with the other pair. Take another piece of copper wire and twist it onto the free end of the iron wire in the same way as the first piece. Use the multimeter on the low resistance scale to ensure good connections. If you can solder, you might want to solder the ends together for a good connection. Place the mug and glass side-by-side and bend the iron wire so that one end hangs into the mug and the other into the glass. Connect the meter to the free ends of the copper wires, and set it to the millivolts range. Fill the glass with water and ice, and the mug with boiling water, and you should get a small voltage reading on the multimeter. Appropriate Technology Appendix - 2 - 3